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Cardiovascular SystemBlood Pressure
Blood Pressure
Definition: The force blood exerts against the inner walls of blood
vessels.Arterial Blood Pressure
Rises and falls in a pattern corresponding to phases of cardiac cycle
Maximum pressure during ventricular contraction is called systolic pressure
When ventricles relax, arterial pressure drops and the lowest pressure is present until the next contraction is called diastolic pressure
BP Cont.
Example:
120/80
Pulse: expanding and recoiling of an artery
Systolic Pressure
Diastolic Pressure
Factors that influence Arterial BP
Heart Action: Determines how much blood enters the arterial system
with each ventricular contractionStroke Volume:
Volume of blood discharged from left ventricle; = about 70 mL in an avg. weight male.
Cardiac Output: Stroke volume/minute
Calculate by multiplying stroke volume by heart rate Example:
If S.V. is 70 mL and heart rate is 72, C.O. is 5,040 mL/min.
BP varies with C.O.; if S.V. or heart rate increase, C.O rises and so does BP; if S.V. or heart rate decreases, C.O and BP decrease.
Blood Volume
Varies with age and sex somewhat; directly with body size
Avg. blood volume is 5 L. or 8% of body weight
B.P. is usually directly proportional to blood volume within cardiovascular system.
Example: A hemorrhage would cause blood loss and cause B.P.
to decrease. Blood volume also falls if fluid volume is upset like in dehydration. Fluid and blood replacement can restore B.P. and volume.
Peripheral Resistance
Friction between blood and walls of blood vessels Factors that change P.R. also change B.P.
Example: Contraction of smooth muscles in arteriolar walls
increase B.P. Dilation of arterioles decrease B.P.
Blood Viscosity
Ease in which fluid molecules flow past one another. Greater viscosity=greater resistance to flow
Blood cells and plasma proteins increase blood viscosity
B.P. increases with increased viscosity and decreases with decreased viscosity.
Control of B.P.
Depends mostly on cardiac output and regulation of peripheral resistance
Cardiac output factors: Starlings Law of the Heart:
Relationship between myocardial fiber length and force of contraction.
Allows heart to maintain a balanced flow of blood. Baroreceptors
Found in walls of aorta and carotid arteries, sense changes in B.P.
SA Node: Increases or decreases heart blood pressure based off
impulse from Medulla Oblongata.
Cardiac Output Factors Cont.
Cardio-inhibitor Reflex: Happens when heart rate decreases and so does
cardiac output and B.P. Returns B.P. back towards normal. Conversely:
Decreasing B.P. initiates cardio-accelerator reflex, SA node received impulse and causes heart to beat faster, increasing cardiac output and restoring pressure.
Other Factors: Emotional responses such as fear and anger Physical exercise Increase in body temp.
Peripheral Resistance Factors
Changes in arteriolar diameter Vasomotor center of Medulla sense changes
in normal B.P. Can send impulses to increase or decrease P.R. by
increasing or decreasing outflow.Certain chemicals
CO2, O2, H ions Influence P.R. by affecting capillary sphincters and
smooth muscles.
Venous Blood Flow
B.P. is low by the time it gets to veins that heart action is only a partial result.
Results from skeletal muscle contraction, breathing movements, and vasoconstriction of veins. As skeletal muscles contract they push against nearby vessels
squeezing blood through vein valves aiding in returning blood back to the heart.
Respiration movements move blood through veins by applying pressure in thoracic cavity
Vasoconstriction return blood to heart by stimulating smooth muscles to contract during low pressure
Veins provide a blood reservoir that adapts to changes in blood volume. If low pressure, vasoconstriction forces extra blood out and to the heart.
BP Chart
Hypertension: Disease known as
high blood pressureHypotension:
Disease known as low blood pressure
Review
What is the relationship between cardiac output and blood pressure?
How does blood volume affect blood pressure?What is the relationship between peripheral
resistance and blood pressure? Between blood viscosity and blood pressure?
What factors affect cardiac output?What is the function of baroreceptors in the walls
of the aorta and carotid artery?How does the vasomotor center control diameters
of arterioles?
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